Electrically shielded module carrier

ABSTRACT

Electric or electronic modules may be carried by an electrically shielded module carrier that includes a cover element and a base element enclosing at least one mounting region which is divided into a front section and a rear section by an intermediate wall card. Holding elements for inserted flat modules are laterally provided in each section and include guiding gratings which face each other in pairs and are integrated into an electromagnetic shield. The cover element and the base element are connected to the guiding gratings of the front section in a fixed manner and are detachably connected to the guiding gratings of the rear section.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to GermanApplication No. 102 30 704.0 filed on Jul. 8, 2002, the contents ofwhich are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an electrically shielded module carrier forreceiving electric and/or electronic modules, the carrier including acover element and a base element, with at least one mounting space,which is divided into a front section and a rear section by anintermediate wall card. Holding elements for inserted flat modules areprovided laterally in each of these sections.

2. Description of the Related Art

Module carriers serve to receive different electric and electronicunits. In many areas of electrical engineering, in particular in thearea of communication technology, the problem arises that in the modulecarrier the mounting space for electronic units has to be protectedagainst parasitic radiation, while electric components, such as fans,power supply units and cabling, also have to be housed in modulecarriers. If these electrical units themselves are not to be consideredto be a source of interference, the manner in which they are housed inthe module carrier requires comparatively fewer shielding measures.

Depending on the type of field to be shielded, different models anddesigns of shielding housing are known in electrical engineering.

To protect against electrostatic effects and slowly variable fields, itis known that the entire housing of an electrical device can be designedin the manner of a Faraday cage. Plate components made of steel,aluminum or special alloys are generally used for shielding devices,assembled using mechanical and electrical connections to form aconductive shielding jacket. Depending on the technical design of theconnections, the mounting space to be protected is ideally field-free.

In the event of incident and emergent electromagnetic waves, the shieldeffect is determined by reflection and transmission at materialinterfaces and by absorption in the shielding wall. In order to satisfythe requirements of a perfect electromagnetic shield, the housingcomponents have to be connected by a plurality of contact points, eachwith the lowest possible contact resistance. Structurally this meansall-round contact of the joint areas with closely spaced contact points.Such all-round contact, which can be achieved by spot welding, screws,rivets, screened springs, contact lugs or flexible sheathed electriccables, requires corresponding expenditure.

A further problem results from the demand for increasing integration andcomponent density. It has to be possible to insert the assembled printedcircuit boards from the front and from the rear into the module frames,i.e. the covers at the front and rear of the module carrier, which areincorporated in the shield, have to be removable. With this model ofmodule carrier the electrical connection of the printed circuit boardsis effected by a connector card arranged across the direction ofinsertion. This connector card, hereafter referred to as theintermediate wall card, is also referred to in the literature as themidplane or double-sided backplane. It is generally arranged in thecenter of the module carrier and is provided with plug-in connectors onboth sides. The printed circuit boards can be pushed into theseconnectors. A shared bus provides an electrical connection between theplug-in modules. The intermediate wall card also often contains activecomponents and it must be accessible or such that it can be disassembledfor service operations.

Given the structure of the module carrier, this means that the mountingspace must be designed as a space with a high level of shielding both inthe front and the rear sections. On the other hand the intermediate wallcard must also be accessible and as simple as possible to mount duringassembly. If, for reasons relating to shielding, the intermediate wallcard also has to be integrated into the shield, the latter must makereliable contact with the shielded housing components.

From an economic point of view shielding costs should where possible betailored to the respective shielding requirements in the module carrier.In other words, where the volume to be mounted is subject to lessstringent requirements with regard to EMC, it should also be possible toreduce costs.

It should also be possible to mass-produce the module carrier, wherepossible with standard production tools.

A module frame with a central backplane is known from EP 0926937. Thebackplane is mounted on a backplane carrier. To mount the backplanethere are two knobs in the central area of the module frame, which serveas axes of rotation and which are arranged both in the cover element andthe base element. These knobs can be inserted by swiveling the backplaneinto cutouts on the backplane carrier, whereby the backplane can bepositioned in the central area of the module frame. Production of themodule frame is comparatively expensive, as the backplane carrierrepresents an additional component with additional production costs.

SUMMARY OF THE INVENTION

An aspect of the invention is to create a module carrier at low cost,with which the mounting space for electronic modules is reliablyshielded from electromagnetic parasitic radiation and which can beproduced economically in large numbers.

It is characteristic of the invention that the printed circuit boardsare held by guiding gratings, which face each other in pairs in themounting space and are integrated into an electromagnetic shield,whereby a cover element and a base element are connected in a fixedmanner to guiding gratings in a front section and detachably to guidinggratings in a rear section.

As the front guiding gratings are connected in a fixed manner to thehousing shells, a preassemblable unit results during production. Thispreassemblable unit significantly facilitates assembly of theintermediate wall card. The intermediate wall card can be inserted intothe mounting space using known handling systems without complicatedswivel movement and be assembled by driver drill. Compared with therelated art there is no need for the backplane carrier and duringassembly there is no need for the complex operation required to snapthis additional component into place. This is advantageous forlarge-scale production.

The guiding gratings on the one hand carry out the function of holdingthe printed circuit boards and form lateral shielding walls with regardto EMC. A plurality of such mounting spaces with a high level ofshielding can be arranged in a laterally adjacent manner on the modulecarrier, each separated by such shielding walls.

In one advantageous embodiment of the invention the sides of both thecover element and the base element are folded in a continuous manner.These folded edges create a mounting space with a lower level ofshielding that is laterally adjacent to the mounting space with a highlevel of shielding for electric modules, e.g. fans, power supply unitsor refrigerator sockets. This mounting space with a lower level ofshielding is less expensive to produce. Shielding costs are bettertailored to shielding requirements.

In one advantageous embodiment of the invention each of the ends of theguiding gratings in the front section facing the intermediate wall cardis provided with an arm and each arm forms a bearing section for theintermediate wall card. This means that the intermediate wall card hasgood contact and can easily be fixed using screws. The screws arepositioned in the insertion direction and are easily accessible forautomatic screwdrivers.

A further improvement in the shield effect is achieved by providing theends of the guiding gratings of the rear section facing the intermediatewall card with tongue-shaped prongs, which engage in correspondingrecesses in the arms and the exit-side ends of the tongue-shaped prongsprojecting from the recesses are subject to plastic deformation. Theplastic deformation can result from stamping, forging or twist-locking.Positive connection of the gratings by twist-locking is preferred. Thetwist-lock connection refers to each prong engaging the edge of therecess assigned to it in the contact area. This airtight connectionensures that the formation of an oxide layer is reliably prevented inthe contact point. The same low level of ohmic resistance is maintainedin the contact point during use. The twist-lock connection can beproduced using an automatic production tool, which grips the end of theprong when the prong is inserted and twists the end. During assemblychamfering of the prongs facilitates insertion into the respectiverecess.

As well as this positive connection it is also conceivable that the endsof the guiding gratings facing the intermediate wall card might overlapand the shielding effect be produced by the overlap.

It is advantageous for the cover element and the base element to bewelded to the guiding gratings of the front section and to be connectedto the guiding gratings in the rear section by a screw connection. Thematerial-positive welded connection not only ensures more reliableelectrical contact but there is also a preassembled unit from theproduction point of view and this is significantly easier to handleduring production than individual parts. Welding can be carried outeconomically using automatic welding tongs, which access the modulecarrier from the front and connect angled elements arranged on the baseand cover sides of the guiding grating respectively to the cover elementor base element. The interval between the weld points can easily bepredefined with automatic welding tools. A weld point interval of around25 mm has proven favorable for many applications in practice as far asEMC is concerned.

If the flat modules are arranged in the mounting space in parallel,horizontal insertion planes, it is favorable to provide recesses on theguiding gratings, which serve as openings for horizontally guidedcooling air. Good heat dissipation from the printed circuit boards canbe achieved by fans housed in a mounting space with a low level ofshielding laterally adjacent to the mounting space with a high level ofshielding.

The shielded module carrier can be produced on a large scale atparticularly low cost, if the shield is made from a metal material withmaterial uniformity in the form of a component produced by a combinedcutting and bending process. Depending on the deployment site, it can befavorable to protect the surface of the components produced by acombined cutting and bending process against corrosion by a galvaniccoating.

Mounting of the preassembled unit can be facilitated by affixing contactstuds or contact lugs pointing in the direction of the joint to theguiding gratings and the folded edges of the housing shells.

The module carrier according to the invention is suitable for differentfields of application in electrical engineering. One particularlypreferred area of deployment is in the 19-inch series, as is generallyused for communication systems.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome more apparent and more readily appreciated from the followingdescription of an exemplary embodiment, taken in conjunction with theaccompanying drawings, of which:

FIG. 1 is a perspective view of the module carrier according to theinvention, in which the upper housing shell has been removed,

FIG. 2 is a perspective view of the module carrier as shown in FIG. 1with the assembled cover element,

FIG. 3 is a perspective view of a greatly enlarged section of the modulecarrier in the area of the connection point between a front and a rearguiding grating,

FIG. 4 is a perspective view of the front guiding grating with recessesfor the prongs of the rear guiding grating,

FIG. 5 is a perspective view of the rear guiding grating withtongue-shaped prongs,

FIG. 6 is a top view of the device according to the invention withouthousing shells.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout.

One exemplary embodiment of the module carrier 1 according to theinvention is shown in the three-dimensional representation in FIG. 1 andFIG. 2. In the drawing in FIG. 1 the cover element 5 is removed and themounting space 2 can be seen. Guiding gratings 7, 7′, 8, 8′ are arrangedfacing each other in pairs on a base element 6. They form lateral limitsof a mounting space 2. An intermediate wall card 3 divides this mountingspace into a front section 9 and a rear section 10. During production ofthe module carrier, in a first stage, the front guiding gratings 7, 7′are connected to the base element 6 and the cover element 5 by spotwelding. Edges folded at right-angles 23 are provided on the cover andbase sides of the guiding gratings for this purpose. The cover element 5and base element 6 are configured as holohedral walls in the area of theshielded space 2.

Centering studs 19 are provided on the cover and base sides of the frontguiding gratings. Centering lugs 12 are also configured on theprojections 11 of the folded edges 4. During assembly the centeringstuds 19 or centering lugs 12 facilitate the mounting of the shieldelements 5, 6, 7, 7′, 8, 8′. Spot welding produces a preassembled unit,including the housing shells 6 and 5 and the front guiding gratings 7and 7′. This preassembled unit facilitates further assembly. Theintermediate wall card 3 can be inserted by automated handling systemsin the rear section 10 and can be fixed to arms 13 of the guidinggratings 7, 7′ using screws. The assembly point of the screw connectionis easily accessible for driver drills, which access from the rearsection 10. The rear guiding gratings 8, 8′ are then screwed to the baseelement 6 and the cover element 5 (FIG. 2) in the rear section 10.

The intermediate wall card 3 is arranged off-center between the frontguiding gratings 7, 7′ and the rear guiding gratings 8, 8′. It extendsin the mounting space 2 across the directions of insertion 20 or 21 andis limited laterally by the guiding gratings. The guiding gratings 7,7′,8,8′ form lateral holding elements for flat modules. These assembledprinted circuit boards can each be inserted in guides in the frontsection 9 or in the rear section 10. The guides can be formed by groovesin the guiding gratings or by guide clips, each of which can be snappedinto the guiding grating. The inserted printed circuit boards arereceived by plug-in connectors arranged on both sides of the card 3. InFIG. 1 the direction of insertion in the front section 9 is marked by anarrow with the reference character 20; the arrow 21 shows the directionof insertion in the rear section 10.

The cover element 5, the base element 6 and the guiding gratings7,7′,8,8′ form sleeve elements of an electromagnetic shielding device,which can be closed off on the front face by front and rear plates (notshown).

As can be seen clearly from the representations in FIG. 1 and FIG. 2,the cover element 5 and base element 6 are each continued laterally inrespect of the mounting space 2 by edges folded at right-angles 4 toform a U-shaped housing shell. This means that a space 22 is enclosed ateach side of the mounting space 2, the shielding effect of which can bedesigned to be different from that of the mounting space 2, depending onrequirements. This lateral space 22 can therefore be shielded to alesser degree compared with the mounting space 2. This can be achievedsimply by making the distance between the contact points of the spotwelds in the joint area of the angled edge 11 larger and achievingcontact with the front-face covers (not shown) at lower cost or moreeconomically. This lateral space 22, which is shielded to a lesserdegree, is very suitable for holding fans, power supply units orcabling. The space 22 forms a shielding prechamber for electromagneticwaves penetrating laterally. The lateral penetration of electromagneticwaves is obstructed by barriers in the form of the angled element 4configured as a perforated wall and the shielding guiding gratings 7 and8 or 7′ and 8′. From a production point of view the lateral extensionsto the housing cover and base elements are simple to produce and caneasily be adapted to different shield effects.

FIG. 3 shows a significantly enlarged representation of a section of themodule carrier 1 in the area of the connection point between a frontguiding grating 7 and a rear guiding grating 8. The end of the rearguiding grating 8 is offset in the direction of insertion and hastongue-shaped prongs 15 at the end. These prongs 15 engage incorresponding recesses 16 (FIG. 4) of an arm 13 of the assigned frontguiding grating 7. Twisting the end of the tongue-shaped prongs 15produces a twist-lock, with which each prong beds into the recess 16,thereby creating an approximately airtight connection at least locallyin the contact area. As shown in FIGS. 1 to 5, the guiding gratings7,7′,8,8′ have recesses 18. These cutouts 18 form openings for a flow ofair guided horizontally in the module carrier. In many applications withan arrangement according to the invention good shielding efficiency canbe achieved if rectangular holes with a diagonal smaller than 25 mm areused.

The folded edges 4 are configured as a perforated plate, with the resultthat lateral air ingress or air egress is possible when module carriersare stacked on top of each other. The many small holes in the perforatedplate are a favorable embodiment for ventilation of the mounting space,as they have a good shielding effect. The form and dimension of theholes 18 are configured according to the electromagnetic waves to bescreened.

FIG. 6 shows a top view of the interior of the shielded space 2, whichis divided by the intermediate wall card 3 into a front section 9 and arear section 10. The guiding gratings 7 and 8 or 7′ and 8′ face eachother in pairs and are arranged in line in the direction of insertion 20and 21. The intermediate wall card 3 is fixed by screw connections ontobearing sections 14 of the front guiding gratings 7, 7′. At their endsfacing the card 3 each of the rear guiding gratings 8, 8′ is offset toproduce prongs 15. The prongs 15 engage in recesses 16 of the guidinggratings 7, 7′. The connection between abutting front and rear guidinggratings is effected by twist-locking the prongs 15 into correspondingrecesses 16. The guiding gratings 7, 7′ are welded along folded edges 23in the front section 9 to the base or cover element; the folded edges 23of the rear guiding grating 8, 8′ are screwed to the cover or baseelement in the rear section 10 by screws with heads or through bolts.The depth of the rear mounting space 9 and therefore also the length ofthe rear guiding gratings 7, 7′ is larger in the exemplary embodimentshown than the depth or length of the guiding gratings 8, 8′ in the rearmounting space 10.

Plug-in connectors are arranged on both sides of the intermediate wallcard 3. The intermediate wall card extends in the mounting space 2across all the plug-in modules and physically provides a communicationchannel between the plug-in modules. It is often equipped with its ownstorage device and/or microprocessor as well as a bus for processing thedata transmission between the plug-in modules. The arrangement in themodule carrier 1 according to the invention allows the intermediate wallcard 3 to be easily accessible for maintenance work due to the easydisassembly of the rear guiding grating 8, 8′.

Naturally a plurality of module carriers according to the invention canbe arranged one on top of the other in a mechanical support, known as arack. The width of such module carriers is generally 19″ (48.3 cm).

The invention has been described in detail with particular reference topreferred embodiments thereof and examples, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention covered by the claims which include the phrase“at least one of A, B and C” as an alternative expression that means oneor more of A, B and C may be used, contrary to the holding in Superguidev. DIRECTV, 69 USPQ2d 1865 (Fed. Cir. 2004).

1-17. (canceled)
 18. An electrically shielded module carrier forreceiving at least one of electric and electronic modules, comprising: acover element and a base element at least partially defining at leastone mounting space; an intermediate wall card dividing the at least onemounting space into a front section and a rear section; and guidinggratings facing each other in pairs, forming lateral holding elementsfor the at least one of electric and electronic modules in each of thefront and rear sections and forming an electromagnetic shield with saidcover element and said base element which are fixedly connected to saidguiding gratings of the front section and are detachably connected tosaid guiding gratings of the rear section.
 19. An electrically shieldedmodule carrier according to claim 18, wherein said cover element andsaid base element form a housing shell and each includes at least onefolded edge.
 20. An electrically shielded module carrier according toclaim 19, wherein said guiding gratings of the front section have endsfacing said intermediate wall card with each end having an arm thatforms a bearing section for said intermediate wall card.
 21. Anelectrically shielded module carrier according to claim 20, furthercomprising at least one screw connection fixedly connecting saidintermediate wall card to the bearing section.
 22. An electricallyshielded module carrier according to claim 21, wherein each arm on theends of said guiding gratings of the front section have recesses, andwherein said guiding gratings of the rear section have ends withtongue-shaped prongs subject to plastic deformation and engaging therecesses of corresponding arms on the ends of said guiding gratings ofthe front section.
 23. An electrically shielded module carrier accordingto claim 22, wherein each of the tongue-shaped prongs has an exit-sideend passing through one of the recesses and twist-locked to engage thecorresponding arms on the ends of said guiding gratings of the frontsection.
 24. An electrically shielded module carrier according to claim23, wherein the exit-side end of each of the tongue-shaped prongs ischamfered.
 25. An electrically shielded module carrier according toclaim 24, wherein said cover element and said base element are welded tosaid guiding gratings in the front section and connected to the guidinggratings in the rear section by at least one screw connection.
 26. Anelectrically shielded module carrier according to claim 25, wherein saidguiding gratings are provided with recesses, which form openings for aflow of air.
 27. An electrically shielded module carrier according toclaim 26, wherein the recesses in said guiding gratings are rectangularwith a diagonal smaller than 25 millimeters.
 28. An electricallyshielded module carrier according to claim 27, wherein said coverelement and said base element are connected by weld points to saidguiding gratings of the front section.
 29. An electrically shieldedmodule carrier according to claim 28, wherein the weld points arearranged at intervals of less than 25 millimeters.
 30. An electricallyshielded module carrier according to claim 29, wherein said coverelement, said base element and said guiding gratings are metallicmaterial with material uniformity after undergoing a combined cuttingand bending process in forming the electromagnetic shield.
 31. Anelectrically shielded module carrier according to claim 30, wherein saidcover element, said base element and said guiding gratings have agalvanic coating
 32. An electrically shielded module carrier accordingto claim 31, wherein the galvanic coating includes zinc.
 33. Anelectrically shielded module carrier according to claim 32, wherein saidguiding gratings have cover and base sides with centering studs.
 34. Anelectrically shielded module carrier according to claim 33, wherein saidintermediate wall card is positioned in the mounting space to produce aninsertion length for the at least one of electric and electronic modulesthat is longer in the front section than in the rear section.
 35. Anelectrically shielded module carrier according to claim 34, wherein theat least one of electric and electronic modules form at least part of acommunication system.
 36. An electrically shielded module carrieraccording to claim 22, wherein the exit-side end of each of thetongue-shaped prongs is chamfered.
 37. An electrically shielded modulecarrier according to claim 20, wherein each arm on the ends of saidguiding gratings of the front section have recesses, and wherein saidguiding gratings of the rear section have ends with tongue-shaped prongssubject to plastic deformation and engaging the recesses ofcorresponding arms on the ends of said guiding gratings of the frontsection.
 38. An electrically shielded module carrier according to claim19, wherein each arm on the ends of said guiding gratings of the frontsection have recesses, and wherein said guiding gratings of the rearsection have ends with tongue-shaped prongs subject to plasticdeformation and engaging the recesses of corresponding arms on the endsof said guiding gratings of the front section.
 39. An electricallyshielded module carrier according to claim 18, wherein said guidinggratings of the front section have ends facing said intermediate wallcard with each end having an arm that forms a bearing section for saidintermediate wall card.